When fluorescent lamps break, fragments of the glass tube, mercury, and powders from the phosphor coating inside the lamp are scattered about. In places where food is processed or stored, and particularly in lighted display cabinets in supermarkets where stocking clerks and customers handle food in proximity to the cabinet lamps, it is at least highly desirable, and is often required by government regulations, that the cabinet lamps be protected in a way that minimizes the possibility of the lamps being broken and if they do break the possibility of glass fragments, mercury, and phosphor powders escaping and contaminating the food. Fluorescent lamps with a protective assembly are known and widely used for this purpose. Examples of such lamps are those described and shown in U.S. Pat. Nos. 4,048,537 (Blaisdell et al., 1977), 4,924,368 (Northrup et al., 1990), and 5,173,637 (Sica, 1992). The Sica patent is owned by the assignee of the present invention.
Store display cabinets for frozen foods present, in addition to the need for minimizing the possibilities of lamp breakage and escape of glass and powders, a requirement for maintaining the optimum light output of the lamp in the low temperature environment; fluorescent lamps designed to operate at ambient room temperature--about 77.degree. F.--provide much less light output at low ambient temperatures than they provide at room temperature. There have, accordingly, been numerous proposals for adapting fluorescent lamps for low-temperature operation, such as those disclosed in the following U.S. Pat. Nos. 2,135,696 (Baumhauser et al., 1938); 2,363,109 (Keiffer, 1944); 2,581,959 (Koehler, 1952); 3,358,167 (Shanks, 1967); 3,453,470 (Hammer, 1969); 3,602,759 (Evans, 1971); 3,720,826 (Gilmore et al., 1973); and 4,916,352 (Haim et al., 1990).
In most instances, the prior art protective assemblies for fluorescent lamps include special molded end fittings that fit onto the terminal caps of the lamp and hold a protective sleeve in place on the lamp. In some cases, the end fittings are intentionally designed so that they can be removed from the lamp, thus allowing the protective assembly to be reused as lamps burn out and are replaced. Removable protective assemblies do not fully ensure that glass fragments and phosphor powders are retained in case the lamp breaks. Also, protective assemblies that are removable permit smoke and fumes that may be present to be drawn in by a convective flow. The contaminants, such as oil, inducted into the space between the lamp and the protective tube produce unsightly deposits and clouding of the tube. Regardless of whether the end fittings are permanently attached to the lamp or are removable, they are relatively expensive and usually have to be designed for a specific lamp style to ensure a proper fit.
The lamp of the Sica patent provides excellent protection against breakage of the lamp, and if the lamp should break, the protective assembly provides an enclosure that is secure against scattering of glass fragments and phosphor powders. In that regard, a protective tube over the lamp tube is securely joined to the terminal caps of the lamp by collars that both mechanically engage and are adhesively secured to the protective tube and the terminal caps. The Sica lamp is inexpensive to produce, inasmuch as it uses simple tubular elements and commercially available adhesives.